• Steel and Composite Structures
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• 제28권2호
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• pp.139-147
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• 2018

Moment frames have considerable ductility against cyclic lateral loads and displacements; however, sometimes this feature causes the relative displacement to exceed the permissible limits. This issue can bring unfavorable hysteretic behavior on the frame due to the reduction in the stiffness and resistance against lateral loads. Most of common bracing systems usually control lateral displacements through increasing stiffness while result in decreasing the capacity for energy absorption. This has direct effect on hysteresis curves of moment frames. Therefore, a system that is capable of both having the capacity of energy absorption as well as controlling the displacements without a considerable increase in the stiffness is quite important. This paper investigates retrofitting of a single-storey steel moment frame using a delayed wire-rope bracing system equipped with the ductile middle steel plate. The steel plate is considered at the middle intersection of wire ropes, where it causes cables to be continuously in tension. This integrated system has the advantage of reducing considerable stiffness of the frame compared to cross bracing systems as a result of which it could also preserve the frame's energy absorption capacity. In this paper, FEM models of a delayed wire-rope bracing system equipped by steel plates with different geometries have been studied, validated, and compared with other researchers' laboratory test results.

• Structural Engineering and Mechanics
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• 제73권3호
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• pp.239-257
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• 2020

In the present study, an innovative steel bracket and haunch hybrid scheme is devised, for retrofitting of earthquake damaged deficient beam-column sub-assemblages. Formulations are presented for evaluating haunch force factor under combined load case of lateral and gravity loads for the design of double haunch retrofit. The strength hierarchies of control and retrofitted beam-column sub-assemblages are established to showcase the efficacy of the retrofit in reversing the undesirable strength hierarchy. Further, the efficacy of the proposed retrofit scheme is demonstrated through experimental investigations carried out on gravity load designed (GLD), non-ductile and ductile detailed beam-column sub-assemblages which were damaged under reverse cyclic loading. The maximum load carried by repaired and retrofitted GLD specimen in positive and negative cycle is 12% and 28% respectively higher than that of the control GLD specimen. Further, the retrofitted GLD specimen sustained load up to drift ratio of 5.88% compared with 2.94% drift sustained by control GLD specimen. Repaired and retrofitted non-ductile specimen, could attain the displacement ductility of three during positive cycle of loading and showed improved ductility well above the expected displacement ductility of three during negative cycle. The hybrid haunch retrofit restored the load carrying capacity of damaged ductile specimen to the original level of control specimen and improved the ductility closer to the expected displacement ductility of five. The total cumulative energy dissipated by repaired and retrofitted GLD, non-ductile and ductile specimens are respectively 6.5 times, 2.31 times, 1.21 times that of the corresponding undamaged control specimens. Further, the damage indices of the repaired and retrofitted specimens are found to be lower than that of the corresponding control specimens. The novel and innovative steel bracket and haunch hybrid retrofit scheme proposed in the present study demonstrated its effectiveness by attaining the required displacement ductility and load carrying capacity and would be an excellent candidate for post-earthquake retrofit of damaged existing RC structures designed according to different design evolutions.

• Structural Engineering and Mechanics
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• 제59권4호
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• pp.653-669
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• 2016

Recent earthquakes worldwide show that a significant portion of the earthquake shaking happens in the vertical direction. This phenomenon has raised significant interests to consider the vertical ground motion during the seismic design and assessment of the structures. Strong vertical ground motions can alter the axial forces in the columns, which might affect the shear capacity of reinforced concrete (RC) members. This is particularly important for non-ductile RC frames, which are very vulnerable to earthquake-induced collapse. This paper presents the detailed nonlinear dynamic analysis to quantify the collapse risk of non-ductile RC frame structures with varying heights. An array of non-ductile RC frame architype buildings located in Los Angeles, California were designed according to the 1967 uniform building code. The seismic responses of the architype buildings subjected to concurrent horizontal and vertical ground motions were analyzed. A comprehensive array of ground motions was selected from the PEER NGA-WEST2 and Iran Strong Motions Network database. Detailed nonlinear dynamic analyses were performed to quantify the collapse fragility curves and collapse margin ratios (CMRs) of the architype buildings. The results show that the vertical ground motions have significant impact on both the local and global responses of non-ductile RC moment frames. Hence, it is crucial to include the combined vertical and horizontal shaking during the seismic design and assessment of non-ductile RC moment frames.

• Structural Engineering and Mechanics
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• 제60권1호
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• pp.51-69
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• 2016

A large number of welded steel moment-resisting framed (SMRF) structures failed due to brittle fracture induced by ductile fracture at beam-to-column connections during 1994 Northridge earthquake and 1995 Kobe (Hyogoken-Nanbu) earthquake. Extensive research efforts have been devoted to clarifying the mechanism of the observed failures and corresponding countermeasures to ensure more ductile design of welded SMRF structures, while limited research on the failure analysis of the ductile cracking was conducted due to lack of computational capacity and proper theoretical models. As the first step to solve this complicated problem, this paper aims to establish a straightforward procedure to simulate ductile cracking of welded joints under monotonic tension. There are two difficulties in achieving the aim of this study, including measurement of true stress-true strain data and ductile fracture parameters of different subzones in a welded joint, such as weld deposit, heat affected zone and the boundary between the two. Butt joints are employed in this study for their simple configuration. Both experimental and numerical studies on two types of butt joints are conducted. The validity of the proposed procedure is proved by comparison between the experimental and numerical results.

• 콘크리트학회논문집
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• 제24권3호
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• pp.341-349
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• 2012

최근 국내외 건축물이 초고층화, 대형화되고 다양화됨으로써 콘크리트의 고성능화가 요구되고 있으며 지진하중과 같은 반복 주기하중이 작용할 때 철근콘크리트 부재의 내진성능의 개선이 필요한 실정이다. 따라서 이 연구에서는 사용성, 안정성 및 신뢰성이 우수한 고연성고내구성을 갖는 최적배합의 고인성 섬유 복합모르타르를 개발하고 플랫 플레이트 슬래브-기둥 접합부의 위험단면영역에 적용하여 건축물의 내력, 연성능력, 에너지소산능력 등의 내진성능을 개선하고 철근콘크리트 건축물의 설계시 기초자료 및 실용화 기술을 제시하고자 한다. 실험 결과 고인성 섬유 복합 모르타르를 활용한 플랫 플레이트 슬래브-기둥 접합부 실험체(RCFPP 시리즈)는 표준실험체(SRCFP)보다 최대내력 15~34%, 연성능력 33~37%, 에너지소산능력은 최대 2.14배 증가함을 나타내었다.

• Steel and Composite Structures
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• 제46권3호
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• pp.417-433
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• 2023

The maximum ductility and cumulative ductility of connection joints of Buckling-Restrained Braced Frames (BRBF) are critical to the structural overall performance, which should be matched with the BRB ductility. The two-story and one-span BRBF with a one-third scale was tested under cyclic quasi-static loading, and the top-flange beam splice (TFBS) rotational connections were proposed and adopted in BRBF. The deformation capacity of TFBS connections was observed during the test, and the relationship between structural global ductility and local connection ductility was studied. The rotational capacity of the beam-column connections and the stability performance of the BRBs are highly relevant to the structural overall performance. The hysteretic curves of BRBF are stable and full under large displacement demand imposed up to 2% story drift, and energy is dissipated as the large plastic deformation developed in the structural components. The BRBs acted as fuses and yielded first, and the cumulative plastic ductility (CPD) of BRBs is 972.6 of the second floor and 439.7 of the first floor, indicating the excellent energy dissipation capacity of BRBs. Structural members with good local ductility ensure the large global ductility of BRBF. The ductile capacity and hysteretic behavior of BRBF with TFBS connections were compared with those of BRBF with Reduced Beam Section (RBS) connections in terms of the experimental results.

• 콘크리트학회논문집
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• 제26권6호
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• pp.695-705
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• 2014

지진구역에 적용하기 위한 연성 강봉을 사용한 프리캐스트 콘크리트 (PC) 보-기둥 접합부를 제안한다. 기존의 DDC 시스템을 활용한 보-기둥 접합부, 파괴모드를 고려해 설계된 두 개의 PC 실험체, 그리고 일체형 RC 실험체가 내진성능를 위해 반복하중 하에서 실험하였다. 실험체는 현행 기준을 만족하도록 설계되었다. 변수는 PC 보 주철근의 항복강도이다. 실험결과 제안된 시스템은 내진기준을 만족하는 것으로 나타났다. 제안된 보-기둥 접합부의 변형능력과 에너지소산 능력은 기존의 DDC 시스템보다 우수한 것으로 나타났다.

• 한국건설순환자원학회논문집
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• 제7권2호
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• pp.158-165
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• 2019

이 연구의 목적은 알칼리활성 슬래그 기반 섬유보강 복합재료를 보 부재의 재료로 활용하였을 때 휨거동을 해석적으로 분석하는 것이다. 7% 이상의 초고연성이 나타날 수 있는 알칼리활성 슬래그 기반 섬유보강 복합재료를 제조하기 위하여 재료 및 배합을 선정하였고, 재료의 압축강도와 인장성능을 평가하였다. 복합재료는 압축강도 32.7MPa, 인장강도 8.43MPa, 인장변형성능 7.52%를 나타내었다. 초고연성 복합재료로 구성된 보의 휨거동을 분석하기 위하여 4가지 단면에 대하여 비선형 단면 층상화 방법을 사용하여 해석을 수행하였다. 해석결과 초고연성 복합재료로 부분적으로 보강된 경우 8.0%, 콘크리트가 복합재료로 전부 치환되어 전체 보강된 경우 24.7%의 휨강도 증진효과가 있는 것으로 나타났다. 휨강도 증진 효과가 크지 않은 이유는 인장 연단의 변형률이 최대 1.38%로 초고연성 복합재료의 인장변형성능의 18.4%밖에 되지 않기 때문인 것으로 나타났다.

• Structural Engineering and Mechanics
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• 제25권1호
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• pp.75-89
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• 2007

Post-earthquake reconnaissance and experimental research indicate that squat reinforced concrete (RC) columns in existing buildings or bridge piers are vulnerable to non-ductile shear failure. Recently, several experimental studies were conducted to investigate upgrading the shear resistance capacity of such columns in order to modify their failure mode to ductile one. Among these upgrading methods is the use of fibre-reinforced polymer (FRP) jackets. One of the preferred analytical tools to simulate the response of frame structures to earthquake loading is the lumped plasticity macromodels due to their computational efficiency and reasonable accuracy. In these models, the columns' nonlinear response is lumped at its ends. The most important input data for such type of models is the element's lateral force-displacement backbone curve. The objective of this study is to verify an analytical method to predict the lateral force-displacement ductility relationship of axially and laterally loaded rectangular RC squat columns retrofitted with FRP composites. The predicted relationship showed good accuracy when compared with tests available in the literature.

• Steel and Composite Structures
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• 제13권4호
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• pp.383-396
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• 2012

In order to develop a verification method for extremely low cycle fatigue (ELCF) of steel structures, the initiation mechanism of ductile cracks is investigated in the present study, which is the first step of brittle fracture, occurred in steel bridge piers with thick-walled sections. For this purpose, a total of six steel columns with small width-thickness ratios were tested under cyclic loading. It is found that ductile cracks occurred at the column base in all the specimens regardless of cyclic loading histories subjected. Moreover, strain history near the crack initiation location is illustrated and an index of energy dissipation amount is proposed to evaluate deformation capacity of structures.